Key Takeaways from METEC and Stanford’s “Single-Blind Determination of Methane Detection Limits and Quantification Accuracy."
A third-party study was recently published evaluating Bridger Photonics’ Gas Mapping LiDAR (GML) first-generation sensors in three performance areas: 1. potential cross-species gas interference, 2. methane detection sensitivity limits, and 3. emission rate quantification accuracy. The study was conducted as a collaboration between Colorado State University’s Methane Emission Technology Evaluation Center (METEC) and Stanford University’s Natural Gas Initiative.
While third-party blind testing doesn’t give the complete picture, it’s important for validating the detection sensitivity performance of emissions detection technologies. This independent study was a robust assessment of GML’s capabilities across a wide range of emission rates and wind speeds. In the study, Bridger performed a total of 650 measurement passes over controlled releases facilitated by METEC/Stanford in Midland, Texas, and Ehrenberg, Arizona for detection sensitivity and quantification studies. A laboratory experiment was also conducted by the group to quantify the potential for cross-species interference with Bridger’s methane measurements.
Here are the key takeaways from the study:
Takeaway 1: GML Achieved a Detection Sensitivity of 1.64 kg/hr with 90% PoD.
The study reports a measured detection sensitivity for the first-generation GML of 0.41 kg/hr per m/s wind speed with 90% probability of detection (PoD) at Bridger’s typical flight altitude of 675’. For typical wind speeds (4 m/s), this equates to 1.64 kg/hr (90% PoD). At 500’ flight altitude, the study found that Bridger achieves 1.0 kg/hr (90% PoD) under these conditions.
To determine the detection sensitivity, METEC/Stanford recorded all of the controlled releases that were either detected (true positives/hits) or not detected (false negatives/misses). There were no false positives. Based on those “hits” and “misses”, the researchers performed a mathematical regression to generate a PoD curve, which provides the probability of detection for a given emission rate with the wind speed normalized.
As an example, from the PoD curve in Figure 2 of the paper (shown below), 0.9 on the left axis, which is a 90% PoD, occurs for an emission rate of 0.41 kg/hr per m/s wind speed. To determine the performance for a particular wind speed, simply multiply that emission rate times the wind speed (in m/s).
Why It Matters:
This study validates Bridger’s stated commercial detection sensitivity for first-generation sensors of 3 kg/hr with a >90% PoD under typical conditions for the production sector. Bridger chooses this detection sensitivity because they have quantitatively estimated that it is sufficient to catch more than 90% of emissions in typical production basins, which helps operators meaningfully yet efficiently reduce emissions. Learn more about emissions distributions here. Bridger’s second-generation sensor (GML 2.0) is projected to achieve <1 kg/hr (90% PoD) to meet all tiers of the EPA’s new methane rule supplement.
Takeaway 2: GML’s Emission Rate Quantification Bias was 8.2%
To test the emission rate quantification capabilities of GML, METEC and Stanford personnel released controlled emissions ranging from 0.17 kg/hr to 1,428 kg/hr. Bridger scanned the releases and reported emission rates, while remaining blind to the metered emission rates on the ground. When using Bridger’s standard wind source, NOAA’s high-resolution rapid refresh (HRRR) wind data source, Bridger’s emission rate quantification bias was measured to be +8.2% for the aggregate set of measurements. The HRRR wind dataset produced the most accurate emission rates among the three wind datasets evaluated in this study.
The plot below shows the reported emission rates vs. controlled released emission rates, and the color of the points corresponds to the windspeed.
Why It Matters:
Accurate quantification of emissions across a wide spectrum of emission rates is critical for methane emissions inventory accounting and for prioritizing emissions to address.
Takeaway 3: GML Exhibits Negligible Cross-Species Gas Interference for Methane Detection
GML was tested for interference with other gases (ethylene, ethane, propane, n-butane, i-butane, and carbon dioxide) that are common to the oil and gas industry. The lab testing identified no significant interference with GML methane measurement.
Why It Matters:
Although other gases may be present on a site, GML scans are tuned to be highly selective for methane. This study found that none of the gases tested have meaningful interference with methane detection and quantification.
Thank you to the teams at METEC, the Stanford Natural Gas Initiative, and other contributing funders including The Environmental Partnership (TEP), and ExxonMobil for this comprehensive and impactful study.
Read the full study linked here.
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